The present invention relates to a metal/silicon multilayer film which undergoes explosive crystallization.
Over 130 years ago, G. Gore first described explosive crystallization in amorphous antimony films. The term "explosive crystallization" describes the rapid exothermic transformation of amorphous materials into their crystalline allotropes. Since Gore's initial description of explosive crystallization, numerous researchers have described explosive crystallization. For example, see Takamori, T. et al., "New Noncrystalline Germanium which Crystallizes "Explosively" at Room Temperature," Appl. Phys. Lett. 20, 201 (1972); Mineo, A. et al., "Velocity of Propagation in the Shock-Crystallization of Sputtered Amorphous Germanium," Solid State Comm. 13, 329 (1973); Wickersham, C. E. et al., "Impulse Stimulated "Explosive" Crystallization of Sputter Deposited Amorphous (In, Ga) Sb Films," Solid State Comm. 27, 17 (1978); and Auvert, G. et al., "Explosive Crystallization of Alpha-Si Films in both the Solid and Liquid Phases," Appl. Phys. Lett. 39, 724 (1981).
However, the commercial application of the phenomenon has been limited Thick coatings have previously been used to demonstrate explosive crystallization at room temperature For example, Koba, R. et al., "Temperature and Thickness Effects on the Explosive Crystallization of Amorphous Germanium Films," Appl. Phys. Lett. 40, 672 (1982) reported that room temperature explosive crystallization in amorphous germanium films requires a germanium film thickness of about 20 microns. A 20 micron thick film is several times more expensive than a film which is less than 1 micron thick.
Koba, R. et al. also reported that the relationship between the film thickness and the minimum ambient temperature required for explosive crystallization had been established using a phenomenological model which had been experimentally confirmed using germanium. The model has also been experimentally confirmed using gallium doped germanium; see Wickersham, C. E. et al., Material Lett. 4, 268 (1986).
In this model, the energy balance condition between the heat generated by the exothermic transformation, the heat loss to the surroundings, and the heat required to continue propagation of the transformation is used to derive a relationship between the film thickness and the minimum ambient temperature for explosive crystallization. The energy balance condition gives Equation (1): EQU T*=T'-H.sub.c /C+(E/C).multidot.1/.lambda.
where T* is the critical temperature for explosive crystallization, T' is the film melting point, H.sub.c is the film heat of crystallization, C is the volume heat capacity of the amorphous film, E is the energy/unit area lost to the surroundings during explosive crystallization, and .lambda.is the total film thickness prior to explosive crystallization. By measuring .lambda.and T* and given T' and C, values for H.sub.c and E can be obtained.
Flora, J., "Propagation of Explosive Crystallization in Thin Rh-Si Multilayer Films," J. Vac. Sci. Technol. A4, 631(1986) reported explosive crystallization in multilayer stacks composed of alternating layers of rhodium and silicon deposited by electron beam evaporation. The multilayer period in the Rh/Si layers studied by Flora ranged from 57.5 to 70nm. No attempt was made by Flora to optimize the multilayer period, nor was any relationship established between multilayer period and total film thickness. Furthermore, rhodium is very expensive.